Crankshafts are used in engines, pumps, compressors, and other mechanical devices for converting reciprocating linear motion into rotational motion, or vice versa. When used in connection with internal combustion engines, crankshafts convert reciprocating linear motion into rotational motion. When used in connection with pumps, crankshafts typically convert rotational motion into reciprocating linear motion.
Tunnel-style crankshafts are a type of crankshaft that are regularly used in reciprocating pumps. These crankshafts include enlarged cheeks or webs for supporting bearings therearound. The webs form the largest diameter of the crankshaft. Main bearings are typically retained in place on the webs with a plurality of retaining elements so as to prohibit or limit any axial movement of the bearing. Tunnel-style crankshafts can be inserted into one-piece, non-split crankcases, as opposed to two-piece, split crankcases as are typically required with most automotive internal combustion engines.
Forces generated by reciprocating pistons or plungers and changes in crank angle can both produce unbalanced shaking moments and unbalanced shaking forces in the pumps. Counterweights are commonly attached to crankshafts in an effort to dynamically balance the crankshafts in order to reduce these undesirable inertial shaking moments and/or forces.